To achieve good glycemic control families of young children with type 1 diabetes mellitus (T1D) must adhere to a well-designed and rigorous treatment regimen. Unfortunately, our research program has published data showing that many young children have glucose levels that exceed pediatric targets and show a high rate of glucose variability. By virtue of their age, size, and developmental status, young children with T1D face many unique challenges to adherence (i.e., increased insulin sensitivity, unpredictable physical activity and food intake, oppositional behavior). We've also identified other barriers to good glycemic control, including mealtime behavior problems, child defiance, and parental stress and fear of hypoglycemia. In order to address these barriers and improve children's glycemic control, we created and tested a parent-based behavioral-nutrition intervention, BEST MEALS. Initial results suggest a mean decrease of 26 mg/dl in young children's daily glycemic levels without increasing hypoglycemia. Building on this success and in response to parents' requests for more assistance delivered in a flexible format that matches their busy lives, in this new study we propose to substantially advance our BEST MEALS intervention through three new design features: 1) new treatment content addressing additional domains of T1D self-care (i.e., insulin use, parental hypoglycemia fear), 2) new child-focused and developmentally targeted treatment content allowing for a family-focused approach and learning activities appropriately matched to each young child's stage of development and readiness to engage in learning about T1D (i.e., helping out with T1D self-care), and 3) a mHealth delivery format using video-based microlectures accessible via the internet to increase scalability and personalized weekly progress reports emailed to families to reinforce the positive changes they make to their child's T1D self-care and glycemia. Thus, our current aims include: 1) to develop DIPPer Academy (Diabetes Information for Parents of Preschoolers), a family-focused mHealth behavioral intervention to promote glycemic control and adherence in young children, 2) to assess relevance, engagement, feasibility, and acceptability of DIPPer Academy through a family-centered iterative design scheme, and 3) to explore the initial efficacy of DIPPer Academy using a randomized, wait-list control design. The project is significant because it directly addresses the limited availability of developmentally-targeted behavioral interventions for families of young children with T1D and proposes to use mHealth to deliver DIPPer Academy thereby making it easier for families to access the treatment and easier to disseminate to other diabetes centers. It is innovative in its plan to include child- focused and developmentally-targeted treatment content in addition to parent treatment content, two treatment tracks based on child age (Li'l DIPPer for children <3 years old and Big DIPPer for 3-5 year olds), and in its plan to use a mHealth delivery format. We expect DIPPer Academy, developed and pilot-tested in this study, will have public health significance by improving health outcomes for young children with T1D.